1. Field of the Invention
The present invention relates to an apparatus and method for driving circuit elements.
2. Description of the Related Art
To apply voltages to two-terminal circuit elements such as coils or resistors, two interconnections are needed for each of the circuit elements. For example, six interconnections are necessary to apply respective voltages to three coils independently.
A lens driver for use in an optical disk drive is one of such apparatuses for applying respective voltages to a plurality of two-terminal circuit elements independently. For example, according to the technique disclosed in Japanese Laid-Open Publication No. 7-65397, the tilt of the optical axis of an optical head with respect to a disk may be corrected by the tilt of an objective lens to be driven by a lens driver.
An apparatus like this drives the objective lens at three degrees of freedom and needs three types of coils. Specifically, this apparatus uses: a tracking coil for driving the objective lens in a tracking direction; a focus coil for driving the objective lens in a focus direction; and a tilt coil for driving the objective lens in such as manner as to tilt the lens with respect to the disk.
These coils are normally energized by way of four electrically conductive springs that support the objective lens thereon. For example, to drive the three coils independently, the tracking and focus coils may be energized by way of the four conductive springs, while the remaining tilt coil may be energized through a fine interconnecting wire that has been extended to an external circuit.
In such a connection, however, the interconnecting wire for energizing the tilt coil unintentionally constitutes a load on the four conductive springs that support the objective lens thereon, thus causing a variation in spring constants disadvantageously. Also, the additional process steps of connecting the interconnecting wire to the tilt coil and fixing the wire in such a manner that the wire places an equal load on the four conductive springs are needed.
This problem may be resolved by connecting the three coils together to a common terminal at one terminal thereof and assigning three interconnecting wires, connected to the those three terminals of the three coils, and one interconnecting wire, connected to the common terminal, to the four conductive springs. In that case, however, the maximum voltage that can be applied to those coils decreases to a half disadvantageously. This phenomenon will be described in further detail below.
Suppose three coils are driven by using a 5 V DC power supply to apply a supply voltage thereto. For example, three coils 102a, 102b and 102c may be connected to three switching elements 101a, 101b and 101c, respectively, as shown in FIG. 18. In that case, six interconnecting wires should be connected in total to the six terminals of the three coils 102a, 102b and 102c. If these switching elements 101a, 101b and 101c are turned ON or OFF so that each of the two terminals of every coil 102a, 102b or 102c may be connected to either the high-potential-level terminal 105H or low-potential-level terminal 105L of the power supply 105, then a voltage of −5 V to 5 V may be created between the two terminals of every coil 102a, 102b or 102c. 
On the other hand, where the three coils 102a, 102b and 102c are connected together at one terminal thereof to a reference potential level as shown in FIG. 19, the three coils 102a, 102b and 102c should be connected at the other terminal thereof to switching elements 103a, 103b and 103c, respectively, so that the other terminal of each of the coils 102a, 102b and 102c may be connected to either the high-potential-level terminal 105H or the low-potential-level terminal 105L of the power supply 105. By providing the common terminal, the number of terminals needed to drive the three coils 102a, 102b and 102c decreases from six to four. In that case, however, if the low-potential-level terminal 105L of the power supply 105 is connected to the reference potential level as indicated by the dashed line 107 in FIG. 19, then the voltage that can be applied to each of the elements (i.e., the coils) is from 0 V to +5 V and the voltage cannot be applied in the reverse direction. To make the voltage applicable in the reverse direction also, the intermediate point of the power supply 105 should be connected to the reference potential level as indicated by the solid line 106 in FIG. 19. Then, the voltage that can be applied to each of the elements (i.e., the coils) is from −2.5 V to +2.5 V.
In this manner, if the three coils are driven by the lens driver with one terminal of each coil connected to the common terminal, then the maximum instantaneous voltage that can be applied to each of those coils decreases to one half. As a result, the thrust on the lens being driven by the coils decreases. For example, if a disk having a track eccentricity greater than its regular value is loaded into such a disk drive, then the thrust on the lens being driven will be short of its required level in the tracking direction. Also, if a disk having a fluttering value greater than its regular value is loaded into such a disk drive, then the thrust on the lens being driven will be short of its required level in the focus direction. In these situations, the disk drive cannot read information from such a disk correctly particularly when the information should be read from the disk at a speed several times as high as the normal one.